1. Field of the Invention
Suspended panel ceilings that extend below a structural ceiling are well-known. Such ceilings have a grid of main beams and cross beams that interconnect to form rectangular openings. The grid is suspended from a structural ceiling by hang wires. Panels are supported in the grid openings on flanges of the beams.
The present invention concerns the design of such suspended ceilings in locations prone to earthquakes.
2. Description of the Related Art
A factor in a suspended ceiling design that is subject to seismic events, is ceiling momentum. During a quake, the suspended ceiling is subject to force vectors that cause oscillations along the main beams, and along the cross beams normal to the main beams. Generally, the larger the connected ceiling area and mass of ceiling, the larger the momentum build-up during a quake. Where the mass of ceiling subject to such momentum build-up exceeds certain limits, the ceiling is likely to collapse.
To control the mass of the ceiling area subject to momentum build-up, building codes generally limit the maximum ceiling segment area for a grid with fixed connections in a suspended ceiling subject to earthquakes, to 2,500 sq. ft. Various methods are used to separate a ceiling that exceeds such limit into such 2,500 sq. foot segments or less, that move in a quake independently of one another, as disclosed, for instance, in co-pending U.S. applications Ser. No. 10,592,614 filed Sep. 12, 2006, and Ser. No. 11/895,986, filed Aug. 27, 2007, incorporated herein by reference.